When welding multiple base materials by arc welding, welding with weaving is employed in which a welding electrode is advanced in the welding direction while performing a sine wave weaving movement to the left and right directions of the weld line. This welding with weaving conventionally has been performed by either oscillating the welding torch itself to the left and right, or tilting to the left and right with the welding torch itself as the center. High trajectory precision is required in a case of an articulated robot performing such welding with weaving.
The following is known art relating to weaving movement.
Japanese Unexamined Patent Application Publication No. 2006-59037 (PTL 1) discloses a welding robot control device which effects sure and precise weaving movement at an amplitude instructed beforehand.
When causing a welding robot to perform weaving movement, angular instruction values are generated for each joint motor based on the instructed weaving frequency and amplitude, and the weaving movement is controlled based on those instruction values. However, the motor is dependent on motor dynamic characteristics (control time constants of feedback system) and cannot move exactly according to the angular instruction values, and consequently cannot weave at the instructed amplitude. The art disclosed in PTL 1 solves this problem as follows. First, the difference in angle instruction values between not performing weaving movement and performing weaving movement is calculated for each joint, as a weaving signal. The gain of the motor feedback system (output amplitude/instructed amplitude) is calculated based on the control time constants of the feedback system of the motor and the weaving frequency, and a value obtained by multiplying the weaving signal by the inverse of the gain is added to the angular instruction value of each joint for when not performing weaving movement, thereby calculating final angular instruction values for each joint.
Also, Japanese Unexamined Patent Application Publication No. 6-222817 (PTL 2) discloses a technology which is applied to a robot that performs welding with weaving, so that a weaving waveform can be traced with precision.
In order to solve the problem of the weaving amplitude changing in a manner dependent on the motor dynamic characteristics, the technology disclosed in PTL 2 obtains a motor drive system model (transfer function G(s)) determined based on the attitude of the robot, and inputs an angular instruction value, obtained by multiplying the angular instruction value for each axis during weaving movement by 1/G(s), to the motor.